1. Technical Field
The present invention relates generally, to voltage regulators and, more particularly, to a digitally controlled multi-phase voltage regulator system to provide power to electronic components, such as microprocessors and the like.
2. Background Information
Electronic components, such as microprocessors require fast, intelligent power systems, typically referred to as voltage regulators (VRs). Voltage delivery must be accurate, precise, and able to respond rapidly to variable current loads.
As electronic components become increasingly powerful, fast and complex, such devices require increasingly capable power supplies. Many devices such as microprocessors, microcontrollers and the like now demand that relatively high current levels be provided extremely efficiently and with very low fluctuations in current and voltage. Microprocessors such as those available from the Intel Corp. and Motorola Inc., for example, can demand a continuous supply of current in excess of 100 amperes at voltage levels below 2 volts.
Conventional power supplies for use in microprocessor systems typically include switched-mode power supplies such as voltage regulator modules (VRMs) or the like operating in a voltage-controlled mode. Each VRM typically controls a voltage across the output load using conventional feedback and compensation circuitry. In such embodiments, the voltage across the load is sensed and compared against a reference signal in the feedback path. The compensation circuitry then controls a gating signal that determines the output voltage as appropriate to provide electrical power to the load component.
To implement such a power supply, a conventional VRM is frequently configured as a conventional step-down buck power converter. A DC load line is often specified for microprocessor loads such that the output load voltage decreases with increasing load current. The scheme of dynamically adjusting the output voltage with load current is commonly referred to as active voltage positioning (AVP). Conventional single-stage buck converters, however, typically do not provide adequate power for many applications due to thermal constraints and efficiency requirements. To overcome this problem, the power supply modules are typically configured as multi-phase converters such that several phase-separated buck channels operate in parallel within the VRM so that load current is appropriately distributed between the various stages. The multiple channels allow for multiphase switching within the power stage to reduce thermal stress, to reduce output ripple voltage and to improve the ability to finely control the electrical output characteristics of the module.
Voltage regulation is achieved by sensing the output voltage via a feedback control loop, which modulates the “ON” time of the high-side switch (PWM) to control the regulated output voltage. Dynamic microprocessor current requirements are roughly 250 A/uSec, resulting in substantial “droop” and “overshoot” of the regulated output voltage. The slew limitations of the power stage, due to the output filter inductance, must be supplemented by microprocessor decoupling capacitors. Due to size and cost restraints, it is not desirable to utilize large quantities of high quality capacitors.
To provide tight voltage regulation and to minimize thermal overstress, it is frequently desired to evenly balance the current provided between the individual channels of the VRM, as well as the current provided between parallel-connected VRMs. To balance the currents provided by the multiple modules and channels, accurate information about the currents provided within the system may be required. Some exemplary current sensing schemes include: (i) measuring voltage across a sense resistor placed in series with the input voltage, (ii) measuring voltage across a high or low-side FET in a buck stage, (iii) measuring voltage across an output inductor, and (iv) using a current sense loop.
Such conventional systems typically implement the VR in either analog components or with a combination of analog and digital components. VR's that implement the control and signaling with a combination of analog and digital components usually perform control digitally and signaling in the analog domain. This combination requires replacement of analog components for performance optimization. Moreover, the use of analog signaling is inferior since it is more susceptible to differential noise pickup which may degrade signal accuracy or precision.
Improved voltage regulator systems and circuits are therefore needed to provide electronic components, such as microprocessors and microcontrollers with a clean supply voltage at high current levels. The ability to maintain supply voltages within a tightly regulated window with rapid variations in current demand is key because of performance and reliability requirements. Conventional voltage regulators are reaching their limits in providing the dual requirements of high current and low voltage.